A reciprocating engine, such as an internal combustion engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. In a typical example, a piston is housed in a sealable piston chamber or pressure chamber, and attached at its base to a rotatable shaft. As the piston slides along the piston chamber, the rotatable shaft is rotated, and vice versa.
An air turbine starter (ATS) can be used to initiate the rotation of the engine. The ATS is often mounted near the engine and can be coupled to a high pressure fluid source, such as compressed air, which impinges upon a turbine wheel in the ATS causing it to rotate at a relatively high rate of speed. The ATS includes an output shaft that is coupled to the turbine wheel and, perhaps via one or more gears, to the engine. The output shaft thus rotates with the turbine wheel. This rotation in turn causes the engine to begin rotating.
The flow of compressed air to the ATS can be controlled by, for example, a valve. This valve is typically referred to as a starter air valve or control valve. When the starter air valve is open, compressed air can flow through the starter air valve, and into the ATS. Conversely, when the starter valve is closed, compressed air flow to the ATS can be prevented. A starter air valve, in many instances, includes a pneumatic actuator to move the valve into its open position. The source of pneumatic power to the actuator can be pressurized air supplied from, for example, an auxiliary power unit (APU), bleed air from another engine compressor, etc.